Glacial epoch and Geological period

Glacial epoch noun - Any period of time during which glaciers covered a large part of the earth's surface.

Geological period and glacial epoch are semantically related. In some cases you can use "Geological period" instead a noun phrase "Glacial epoch".

Geological period noun - A unit of geological time during which a system of rocks formed.

Glacial epoch and geological period are semantically related. Sometimes you can replace phrase "Glacial epoch" with "Geological period", this phrases are similar.